1. Field of the Invention
The present invention relates to a cold cathode ionization vacuum gauge and an inner wall protection member for protecting the inner wall of a cathode of the cold cathode ionization vacuum gauge.
2. Description of the Related Art
A cold cathode ionization vacuum gauge is a device which measures the pressure in a vacuum chamber constituting a vacuum processing apparatus by inducing ionization of gas through self-discharge between a anode and a cathode. Heretofore, a Penning type cold cathode ionization vacuum gauges, a magnetron type cold cathode ionization vacuum gauges, and an inverted magnetron type cold cathode ionization vacuum gauge have been known (see Patent Document 1). The magnetron type cold cathode ionization vacuum gauge and the inverted magnetron type cold cathode ionization vacuum gauge are particularly suitable for measurement in a high vacuum range since they have structures that offer high electron trap efficiency and are capable of stable and continuous discharge even in a high vacuum range.
Meanwhile, it is known that a cold cathode ionization vacuum gauge causes a self-sputtering effect during use and thereby produces an insulative film mainly containing the material of a gauge head container over the inner wall of this container. The insulative film produced on the inner wall possibly inhibits the discharge and deteriorates the pressure measurement accuracy. For this reason, regular maintenance is required.
In view of this, in a cold cathode ionization vacuum gauge described in Patent Document 2, adhesion of an insulative film to the inner wall of a cathode (gauge head container) is prevented by a tubular spacer mounted in such a way as to cover the inner side of the gauge head container. Moreover, the maintainability is improved by a structure in which ignition assist members for improving the discharge characteristics are sandwiched between and supported by the cylindrical spacer and metal blocks. The tubular spacer is made of a metal material such as stainless steel.
The related art is as follows.
[Patent Document 1] Japanese Patent Application Publication No. Hei 10-19711
[Patent Document 2] Japanese Patent Application Publication No. 2008-304361
As described above, in the technique disclosed in Patent Document 2, the tubular spacer is provided to protect the inner wall of the gauge head container from a sputtering effect by plasma generated in a discharge space and from production of adhering matters by the sputtering. Specifically, the spacer is provided in such a way as to cover the inner wall of the gauge head container serving as a cathode and having a hollow portion, and a shaft electrode serving as an anode is inserted in a hollow portion of the spacer. Thus, the hollow portion of the tubular spacer serves as the discharge space. However, the spacer is required to have high rigidity and its thickness is therefore large. The thicker the spacer, the smaller the discharge space becomes. Hence, in order to secure a desired size of a discharge space excluding the spacer, the diameter of the gauge head container must be increased with the thick spacer taken into consideration. This in turn leads to increase in size of the apparatus. In other words, in order to obtain a discharge space of a predetermined size, the size of the gauge head container needs to be increased by the size of the thick spacer.
Moreover, in a case where the diameter of the tubular spacer is smaller than its design value, backlash of the spacer sometimes occurs. In this case, the spacer must be aligned by using an O-ring or the like to fill a gap, which is a cause of the backlash, formed between the spacer and the inner wall of the gauge head container.